The present invention relates to instrumented rolling bearings provided with a system for detecting rotation parameters such as angular position, rotation direction, speed and acceleration.
Instrumented rolling bearings and systems of the above kind are well known to the person skilled in the art, for example from the document FR-A-2 754 903. Instrumented rolling bearings can be used in the control of synchronous electric motors, for example, where it is desirable to know the relative angular position of the rotor poles and the stator poles, especially to determine when the rotor poles are aligned with the stator poles, as in this position the output torque is at a maximum.
The detector system comprising a sensor unit and an encoder supplies the motor control system with all the necessary information, in particular the rotation speed and the position of the rotor poles relative to the stator poles.
A rotatable part can be fitted with an encoder delivering pulses and a non-rotatable part can be fitted with a fixed sensor adapted to detect the pulses and to deduce therefrom information relating to movement of the rotatable part and its angular position relative to the non-rotatable part. In the conventional arrangement, the sensor-encoder system is independent of the rolling bearings enabling one part to rotate inside another part concentric with it.
The encoder can be a magnetic encoder in the form of a multipole ring in which the number of poles depends on the number of poles of the motor to be controlled. This is known in the art. The encoder can cooperate with a magnetosensitive sensor, for example a Hall effect sensor, delivering an output voltage varying on each change of polarity of the ring of the encoder and thus delivering a characteristic squarewave signal.
Using an instrumented rolling bearing provided with an encoder fastened to the rotatable race of the rolling bearing and a sensor fastened to the non-rotatable race of the same rolling bearing is also known in the art. A connector and a cable connect the sensor to an electronic unit which continuously analyzes and processes the signal coming from the sensor.
Compared to a conventional arrangement using a sensor/encoder detector system independent of the rolling bearing, using an instrumented rolling bearing offers substantial advantages for the end user, in particular with regard to compactness and the small number of parts, which facilitates installation.
In order to be able to determine the position of the rotor poles relative to those of the stator by means of the instrumented rolling bearing, it is clear that, when installing the rotor in the stator:
the sensor must be oriented angularly relative to the poles of the stator,
the encoder must be oriented angularly relative to the sensor, and
the encoder must be oriented angularly relative to the poles of the rotor.
These operations are relatively difficult because they must be carried out simultaneously during installation of the rotor in the stator. Mechanical or optical indexing means must be used when installing the rolling bearing in the electric motor to ensure simultaneous adequate relative angular orientation of the aforementioned components so that the signal from the instrumented rolling bearing can be used subsequently to identify the angular position of the rotor poles relative to the stator poles.
The present invention proposes an instrumented rolling bearing which is substituted for one of the two rolling bearings, thereby avoiding the need to install a separate sensor-encoder system in the motor, said instrumented rolling bearing further relieving the user of any need to index the encoder relative to the sensor and relative to the rotor poles during final installation in the motor.
An instrumented antifriction rolling bearing in accordance with one aspect of the invention includes a non-rotatable part comprising a non-rotatable race and sensor means, a rotatable part comprising a rotatable race and encoding means, and a row of rolling bodies arranged between two raceways of the non-rotatable ring and the rotatable ring. The non-rotatable sensing means and the rotatable encoding means form a system for detecting rotation parameters. The rolling bearing comprises temporary retaining beans for temporarily maintaining the angular indexing of the encoding means relative to the sensing means, in an angular position wherein said encoding means generate a reference signal in the sensing means.
The part that moves axially is advantageously adapted to be fastened to the rotatable part of the bearing.
In one embodiment of the invention the part that moves axially toward the row of rolling bodies is a support of the encoder means.
In another embodiment of the invention the part that moves axially toward the row of rolling bodies is mounted on a support of the encoder means.
In another embodiment of the invention the part that moves axially toward the row of rolling bodies is a member mounted on the rotatable race of the rolling bearing on the side opposite the encoder means.
The temporary retaining means are preferably active during transportation, manipulation and installation of the rolling bearing until it is permanently fixed into its housing and to the shaft.
Said temporary retaining means are advantageously part of said detector system. Said temporary retaining means can be fastened to a cap for protecting the sensor means.
In one embodiment of the invention said temporary retaining means comprise a friction member, for example in the form of elastomer pads, for example rubber pads.
In one embodiment of the invention the encoder means comprise a support. Said support has a first surface in axial contact with the rotatable race and a second surface axially opposite the first surface and in axial contact with the non-rotatable part.
Said support can be annular and made of sheet metal and have a radial or frustoconical portion including said first surface, a cylindrical portion and a radial portion including said second surface and extending toward said sensor means.
In one embodiment of the invention the coefficient of friction between the first surface of said support and the rotatable race is lower than that between the second surface and the non-rotatable part, so that said support is constrained to rotate with the non-rotatable part when the temporary retaining means are active. The contact between the second surface and the non-rotatable part can be a metal-to-metal contact and the contact between the first surface and the rotatable race can be a rubber-to-metal or rubber-to-rubber contact.
Said temporary retaining means advantageously comprise a weak member. It can be broken by applying a particular axial force to the encoder means or its support, for example when clamping the rolling bearing onto a shaft for supporting it.
In one embodiment of the invention the encoder means include a support having a connecting portion connecting it to the non-rotatable part. The connecting portion is fastened to the support of the encoder means and of the non-rotatable part before the weak member is broken, and has a mechanically weak area adapted to break to separate the encoder means from the non-rotatable part.
The connecting portion can be between a radial portion of a protective cap for the sensor means and a radial portion of the support for the encoder means, the connecting portion being formed in an annular space between them. Said radial portions can be coplanar before the weak member is broken. The connecting portion can be molded over both of said radial portions.
In one embodiment of the invention the mechanically weak area comprises a plurality of synthetic material studs.
In one embodiment of the invention the support of the encoder means is in one piece.
In another embodiment of the invention the support of the encoder means is in two parts at least one of which is in direct contact with the encoder means and at least one of which is in direct contact with the temporary retaining means. The two parts can be concentric and fit together with friction contact. The two parts can be connected temporarily by weak studs.
In one embodiment of the invention the support of the encoder means has at least one axially deformable portion.
In one embodiment of the invention, the retaining means are in one piece.
In another embodiment of the invention, the retaining means are in two parts which are advantageously concentric and joined temporarily by weak studs.
In one embodiment of the invention, the retaining means are generally annular.
More generally, means are provided for releasing the temporarily fixed angular indexing by axial displacement of at least one portion of one component of the system in the direction of the row of rolling bodies. The releasing means are associated with the retaining means and break the coupling by moving the two coupled components axially. Radial friction surfaces are moved apart, weak portions are broken, etc. Said releasing means include an axial space to allow said axial displacement.
The present invention also proposes a method of installing an instrumented rolling bearing on a shaft. The rolling bearing is of the type having a non-rotatable part comprising a non-rotatable race and sensor means, a rotatable part comprising a rotatable race and encoder means, and a row of rolling bodies disposed between two rolling paths of the non-rotatable and rotatable races, the non-rotatable sensor means and the rotatable encoder means forming a rotation parameter detector system. Prior to installation, the encoder means are retained relative to the sensor means in an angular position in which said encoder means generate a reference signal in the sensor means. During clamping of the rolling bearing on the shaft, the encoder meals and the rotatable race of the rolling bearing are fastened together circumferentially, and the retention of the angular position of the encoder means relative to the sensor mean, is eliminated.
The temporarily fixed angular indexing is released by axial displacement of at least one portion of a component of the system toward the row of rolling bodies.
The encoder support is advantageously detached from the retaining means by axial displacement when attaching the encoder means to the rotatable race of the rolling bearing. Alternatively, the encoder support is detached from the retaining means by rotating the rotatable race.
The sensor means can of course comprise one or more sensors, in particular to increase the resolution and to determine a rotation direction. The sensor means can be magnetic or optical.